What the Chargers offensive line will look like in 2013, it's too early to tell.

But there will be competition.

The team signed guard Rich Ohrnberger to a one-year contract Thursday. A four-game starter with the Cardinals last season, he joins the mix of interior linemen who will compete for a roster spot and role in training camp.

Ohrnberger, 27, is the third offensive lineman the Chargers have added in free agency.

Two of his starts in 2012 came at right guard, his primary position. He also filled in twice at center before a season-ending knee injury.

The Patriots drafted him in the 2009 fourth round and waived him after a head injury sidelined him in 2011. The 6-foot-2, 300-pound veteran has appeared in 18 career games.

Tackle King Dunlap and guard Chad Rinehart are the other offensive linemen the Chargers have signed since March 12. It's been about making the most with what the team has, which is a limitation in funds relative to the salary cap.

The Chargers had $7.5 million in space prior to Wednesday's Danny Woodhead signing.

Ohrnberger finds some familiarity in San Diego. He reunites with offensive coordinator Ken Whisenhunt, who coached the Cardinals last year, and guard Johnnie Troutman, a former Penn State teammate.

Troutman missed his 2012 rookie season while recovering from pectoral surgery. The fifth-round draft pick is expected to compete for a starting job.

San Diego is expected to further address the offensive line in the draft. It has seven assigned selections at picks No. 11, 45, 76, 110, 145, 179 and 221. The Chargers were not awarded any compensatory selections this week, something they anticipated following last year's active free agency.